Particle Physics

We present a short review of the local conformal symmetry and its anomalous violation in curved $4d$ space-time. Furthermore we discuss the ambiguities of conformal anomaly and the anomaly-induced effective actions. Despite the conformal symmetry is always broken at quantum level, it is useful for constructing the best known approximations for investigating quantum corrections to the classical action of gravity. These quantum corrections represent an appropriate basis for a number of applications in cosmology and black hole physics.

We use black holes to understand some basic properties of theories of quantum gravity. First, we apply ideas from black hole physics to the physics of accelerated observers to show that the equations of motion of generalized theories of gravity are equivalent to the thermodynamic relation $\delta Q = T \delta S$. Our proof relies on extending previous arguments by using a more general definition of the Noether charge entropy. We have thus completed the implementation of Jacobson's proposal to express Einstein's equations as a thermodynamic equation of state. Additionally, we find that the Noether charge entropy obeys the second law of thermodynamics if the energy momentum tensor obeys the null energy condition. Our results support the idea that gravitation on a macroscopic scale is a manifestation of the thermodynamics of the vacuum. Then, we show that the existence of semiclassical black holes of size as small as a minimal length scale l_{UV} implies a bound on a gravitational analogue of 't-Hooft's coupling $\lambda_G(l)\equiv N(l) G_N/l^2$ at all scales $l \ge l_{UV}$. The proof is valid for any metric theory of gravity that consistently extends Einstein's gravity and is based on two assumptions about semiclassical black holes: i) that they emit as black bodies, and ii) that they are perfect quantum emitters. The examples of higher dimensional gravity and of weakly coupled string theory are used to explicitly check our assumptions and to verify that the proposed bound holds. Finally, we discuss some consequences of the bound for theories of quantum gravity in general and for string theory in particular.

The screening of electric charge in plasma with Bose condensate of a charged scalar field is calculated. In all previous calculations before 2009 the effects of Bose condensation have not been considered. Due to the condensate the time-time component of the photon polarization tensor in addition to the usual terms k-squared and Debye mass squared, contains infrared singular terms inversely proportional to k and k-squared. Such terms lead to power law oscillation behaviour of the screened potential, which is different form Friedel oscillations known for fermions. An analogue of Friedel oscillations in bosonic case is also considered.

The Standard model of Cosmology consists of a package of ideas that include Cold Dark Matter, Inflation, and the existence of a small Cosmological Constant. While there is no consensus about what lies beyond the Standard Model, there is a leading candidate that also includes a small package of ideas: A Landscape of connected vacua: the idea that the universe started out with a large energy density, and Coleman DeLuccia Tunneling between vacua. An additional idea that comes from string theory and black hole physics is the Holographic Principle. I will explain how the various ingredients for a "post-standard-model" standard model fit together.

We understand the history of our universe very well but remain ignorant on one key question: what is most of the universe actually made of? Beautiful measurements, by satellites, balloon-basted observatories, the Hubble telescope and ground-based telescopes have allowed us to accurately trace this history of the history of the ordinary matter we are made of. Yet these measurements also show us that most of the universe is dark - that is to say it cannot be seen visibly no matter how bright a light is shone on it. I will discuss why we think that 95% of the universe is dark and will show how we are trying to directly observe dark matter. I will explain what it is like to do science underground and why we need to be so deep to make these measurements.

Recently there has been renewed interest in cosmological gravity, namely 3d gravity coupled to a Chern-Simons term with parameter $\mu$, following claims that at $\mu =1$ the theory becomes chiral and stable. In this talk we will investigate cosmological gravity by setting up a concrete holographic dictionary with a dual 2d field theory and we will demonstrate that the theory is in fact not chiral in the limit $\mu = 1$. Instead our holographic dictionary implies that at $\mu =1$ the dual field theory becomes a logarithmic CFT (LCFT). Our results resolve confusions in the earlier literature and the resulting new class of holographic dualities involving LCFTs may have interesting applications to strongly correlated condensed matter systems.

Cosmological bubble collisions arising from first order phase transitions are a generic consequence of the Eternal Inflation scenario. I will present our computational strategy for generating and evolving these bubbles in 3+1 dimensions and in a self-consistently expanding background. I will show the existence of classical field transitions--the classical nucleation of bubbles during collisions--which can dramatically alter the canonical description of eternal inflation.

We propose a holographic description of four dimensional single scalar inflationary universes, in particular asymptotically de Sitter cosmologies and power-law inflation. We show how cosmological observables such as the primordial power spectrum and non-gaussianities are encoded in correlation functions of a three dimensional QFT.